Power amplifier circuit

ABSTRACT

A power amplifier circuit includes a lower transistor having a first terminal, a second terminal connected to ground, and a third terminal, wherein a first power supply voltage is supplied to the first terminal, and an input signal is supplied to the third terminal; a first capacitor; an upper transistor having a first terminal, a second terminal connected to the first terminal of the lower transistor via the first capacitor, and a third terminal, wherein a second power supply voltage is supplied to the first terminal, an amplified signal is outputted to an output terminal from the first terminal, and a driving voltage is supplied to the third terminal; a first inductor that connects the second terminal of the upper transistor to ground; a voltage regulator circuit; and at least one termination circuit that short-circuits an even-order harmonic or odd-order harmonic of the amplified signal to ground potential.

This application claims priority from Japanese Patent Application No.2018-165368 filed on Sep. 4, 2018. The content of this application isincorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates to a power amplifier circuit.

2. Description of the Related Art

In power amplifier circuits mounted in mobile communication devices suchas mobile phones, there is a demand for increased the maximum outputpower of transmit signals to be transmitted to base stations. Forexample, Japanese Unexamined Patent Application Publication No.2018-85689 discloses a power amplifier circuit in which two transistorsare vertically connected to each other. In the disclosed power amplifiercircuit, the upper and lower transistors are connected to each other viaa capacitor, and the emitter of the upper transistor is grounded via aninductor, thereby rendering the upper and lower transistors conductivefor alternating current and cut-off for direct current. Accordingly, asignal having a voltage amplitude that is about twice as high as thepower supply voltage is outputted from the collector of the uppertransistor, and the maximum output power is increased.

There is also a demand to reduce the power consumption of mobilecommunication devices carried by users. In particular, power amplifiercircuits have relatively high power consumption, and thereforeimprovement in power-added efficiency (PAE) is important. For example,“Progress of the Linear RF Power Amplifier for Mobile Phones” by SatoshiTANAKA, IEICE Transactions on Fundamentals of Electronics,Communications and Computer Sciences, Vol. E101.A, No. 2, 2018, pp.385-395 (hereinafter referred to as “Non-Patent Document”) discloses aconfiguration in which harmonics of a transmit signal are controlled sothat the even-order harmonics are short-circuited to ground potentialand the odd-order harmonics are made open-circuited to allow a poweramplifier to operate in a class-F mode. The class-F operation is knownas a technology for providing both high linearity and high efficiencyfor power amplifiers.

However, the solution described in Non-Patent Document to improvepower-added efficiency is not necessarily sufficient for the poweramplifier circuit described in Japanese Unexamined Patent ApplicationPublication No. 2018-85689.

BRIEF SUMMARY OF THE DISCLOSURE

Accordingly, it is an object of the present disclosure to provide apower amplifier circuit with improved power-added efficiency that canincrease the maximum output power.

According to preferred embodiments of the present disclosure, a poweramplifier circuit includes a lower transistor having a first terminal(collector), a second terminal (emitter), and a third terminal (base),wherein a first power supply voltage is supplied to the first terminal(collector), the second terminal (emitter) is connected to ground, andan input signal is supplied to the third terminal (base); a firstcapacitor; an upper transistor having a first terminal (collector), asecond terminal (emitter), and a third terminal (base), wherein a secondpower supply voltage is supplied to the first terminal (collector), anamplified signal obtained by amplifying the input signal is output to anoutput terminal from the first terminal (collector), the second terminal(emitter) is connected to the first terminal (collector) of the lowertransistor via the first capacitor, and a driving voltage is supplied tothe third terminal (base); a first inductor that connects the secondterminal (emitter) of the upper transistor to ground; a voltageregulator circuit; and at least one termination circuit thatshort-circuits one of an even-order harmonic or an odd-order harmonic ofthe amplified signal to ground potential. The at least one terminationcircuit is disposed so as to branch off from a node along a transmissionpath extending from the first terminal (collector) of the lowertransistor to the output terminal through the first capacitor and theupper transistor.

According to preferred embodiments of the present disclosure, it may bepossible to provide a power amplifier circuit with improved power-addedefficiency that can increase the maximum output power.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of preferred embodiments of the present disclosure withreference to the attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates an example configuration of a power amplifier circuitaccording to a first embodiment of the present disclosure;

FIG. 2A illustrates a specific example of a termination circuit;

FIG. 2B illustrates a specific example of a filter circuit;

FIG. 3A is a graph illustrating the frequency characteristic of theimpedance of the termination circuit;

FIG. 3B is a graph illustrating the frequency characteristic of theimpedance of the filter circuit;

FIG. 4 illustrates waveforms of the collector voltage and collectorcurrent of an amplifier when operating in a class-F mode;

FIG. 5 illustrates an example configuration of a power amplifier circuitaccording to a second embodiment of the present disclosure;

FIG. 6 illustrates an example configuration of a power amplifier circuitaccording to a third embodiment of the present disclosure;

FIG. 7 is a graph illustrating the frequency characteristic of theattenuation of an output signal in a power amplifier circuit accordingto a fourth embodiment of the present disclosure;

FIG. 8 illustrates an example configuration of a power amplifier circuitaccording to a fifth embodiment of the present disclosure;

FIG. 9 is a graph illustrating the frequency characteristic of theattenuation of an output signal in the power amplifier circuitillustrated in FIG. 8;

FIG. 10 illustrates an example configuration of a power amplifiercircuit according to a sixth embodiment of the present disclosure;

FIG. 11 illustrates an example configuration of a power amplifiercircuit according to a seventh embodiment of the present disclosure;

FIG. 12 illustrates an example configuration of a power amplifiercircuit according to an eighth embodiment of the present disclosure; and

FIG. 13 is a graph illustrating the frequency characteristic of thetransmission attenuation of an output signal in the power amplifiercircuit illustrated in FIG. 12.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following describes embodiments of the present disclosure in detailwith reference to the drawings. The same or substantially the sameelements are denoted by the same numerals, and will not be repeatedlydescribed.

FIG. 1 illustrates an example configuration of a power amplifier circuit100A according to a first embodiment of the present disclosure. Thepower amplifier circuit 100A is mounted in, for example, a mobilecommunication device such as a mobile phone, and is configured toamplify an input radio frequency (RF) signal RFin and to output anamplified signal RFout. The RF signal RFin has a frequency of aboutseveral to several tens of gigahertz (GHz), for example.

As illustrated in FIG. 1, the power amplifier circuit 100A includes, forexample, transistors 110 and 111, bias circuits 120 and 121, a voltageregulator circuit 130, capacitors 140 and 141, inductors 150 to 152,matching networks (MNs) 160 and 161, a termination circuit 170, and afilter circuit 180.

The transistors 110 and 111 are each constituted by a bipolar transistorsuch as a heterojunction bipolar transistor (HBT). The transistors 110and 111 are not limited to bipolar transistors, and may be eachconstituted by a field-effect transistor such as ametal-oxide-semiconductor field-effect transistor (MOSFET). In thiscase, the terms “collector”, “base”, and “emitter” are changed to theterms “drain”, “gate”, and “source”, respectively. In the followingdescription, the two transistors 110 and 111 are sometimes referred tocollectively as an “amplifier”.

A power supply voltage Vcc1 (first power supply voltage) is supplied toa collector (first terminal) of the transistor 110 (lower transistor)via the inductor 150. The RF signal RFin (input signal) is supplied to abase (third terminal) of the transistor 110 via the matching network 160and the capacitor 140. An emitter (second terminal) of the transistor110 is grounded. The base of the transistor 110 is also supplied with abias current or bias voltage outputted from the bias circuit 120.Accordingly, an amplified signal obtained by amplifying the RF signalRFin is outputted from the collector of the transistor 110.

A power supply voltage Vcc2 (second power supply voltage) is supplied toa collector (first terminal) of the transistor 111 (upper transistor)via the inductor 151. A bias current or bias voltage outputted from thebias circuit 121 is supplied to a base (third terminal) of thetransistor 111 via the voltage regulator circuit 130. An emitter (secondterminal) of the transistor 111 is grounded via the inductor 152. Theemitter of the transistor 111 is connected to the collector of thetransistor 110 via the capacitor 141. Accordingly, the amplified signalRFout, which is obtained by amplifying the RF signal RFin, is outputtedto an output terminal T from the collector of the transistor 111.

The capacitor 141 (first capacitor) connects the emitter of the uppertransistor 111 and the collector of the lower transistor 110. Thecapacitor 141 has a function of isolating the upper transistor 111 andthe lower transistor 110 from each other for direct current andconnecting the upper transistor 111 and the lower transistor 110 to eachother for alternating current.

The inductor 152 (first inductor) has an end connected to the emitter ofthe transistor 111 and another end grounded. The inductor 152 has afunction of connecting the emitter of the upper transistor 111 to groundfor direct current.

The effect of the connection of the transistors 110 and 111, thecapacitor 141, and the inductor 152 in the manner described above willbe described, assuming that the power supply voltages Vcc1 and Vcc2 areeach 3 V.

Since the power supply voltage Vcc1 (DC3V) is supplied to the collectorof the lower transistor 110 for direct current, the collector voltage ofthe lower transistor 110 varies in a range of DC3V±AC3V. The emittervoltage of the upper transistor 111 varies in a range of DC0V±AC3V sincethe emitter of the upper transistor 111 is grounded for direct currentand is connected to the collector of the lower transistor 110 foralternating current. The collector voltage of the transistor 111 variesin a range of DC3V±AC6V since the power supply voltage Vcc2 (DC3V) issupplied to the collector of the transistor 111 for direct current andthe signal amplitudes at the collector and emitter of the transistor 111are added together for alternating current. Accordingly, the signalamplitude across the collector and emitter of the upper transistor 111is the same as the signal amplitude across the collector and emitter ofthe lower transistor 110, whereas the signal amplitude at the collectorof the upper transistor 111 is about twice as high as the signalamplitude across the collector and emitter.

Given that the output power of a signal is denoted by P, the collectorvoltage by V, and the load impedance of the amplifier by R, then, arelation of P=V²/R holds. In this case, in order to double the voltageamplitude and double the output power, the load impedance is doubled. Inthe power amplifier circuit 100A, accordingly, the load impedance can bedoubled without increasing the power supply voltage, and the maximumoutput power of a signal can be increased, compared to a configurationin which transistors are not vertically connected to each other.

The bias circuits 120 and 121 generate a bias current or bias voltageand supply the bias current or bias voltage to the bases of thetransistors 110 and 111, respectively. The configuration of the biascircuits 120 and 121 is not limited to any specific one, and will not bedescribed in detail.

The voltage regulator circuit 130 is disposed between the bias circuit121 and the base of the upper transistor 111. In this embodiment, thevoltage regulator circuit 130 includes an inductor 153 and a capacitor142, which are connected in series. A bias current is supplied to an endof the inductor 153 from the bias circuit 121. The other end of theinductor 153 is connected to the base of the upper transistor 111. Thecapacitor 142 has an end connected to the base of the upper transistor111 and another end grounded.

The voltage regulator circuit 130 adjusts the impedance seen from thebase terminal of the transistor 111 so that operations based on theamplitude of the voltage (driving voltage) to be supplied to the base ofthe transistor 111 are not restricted by the bias circuit 121. That is,in order to turn on the upper transistor 111, the base-emitter voltageof the transistor 111 needs to be greater than or equal to apredetermined voltage. Accordingly, the base voltage of the transistor111 needs to vary with the emitter voltage of the transistor 111. Thevoltage regulator circuit 130 including the capacitor 142 functions tomake the base voltage of the transistor 111 vary for alternatingcurrent. The capacitance value of the capacitor 142 is preferablysmaller than the capacitance value of the capacitor 141. This is becausean excessively large capacitance value of the capacitor 142 suppressesthe variation of the base voltage of the transistor 111.

The capacitor 140 removes the direct current component of an RF signal.Each of the inductors 150 and 151 suppresses coupling of an RF signal toa power supply circuit (not illustrated).

The matching networks 160 and 161 each match the impedances of thepreceding and subsequent circuits. Each of the matching networks 160 and161 is constituted by an inductor and/or a capacitor, for example.

The termination circuit 170 is disposed so as to branch off from a nodealong a transmission path L (see the broken line in FIG. 1) extendingfrom the collector of the lower transistor 110 to the output terminal Tthrough the capacitor 141 and the upper transistor 111, the node beingpositioned between the collector of the transistor 111 and the matchingnetwork 161. In this embodiment, the termination circuit 170 isconstituted by, for example, a notch filter circuit that short-circuitsthe second-order harmonic of the amplified signal RFout to groundpotential (i.e., terminates the harmonic with low impedance).

FIG. 2A illustrates a specific example of the termination circuit 170.In FIG. 2A and FIG. 2B described below, a termination circuit and afilter circuit are each constituted by a lumped constant circuit, by wayof example. However, a termination circuit and a filter circuit may beeach constituted by a transmission line instead of a lumped constantcircuit. FIG. 3A is a graph illustrating the frequency characteristic ofthe impedance of the termination circuit 170. In the graph illustratedin FIG. 3A, the vertical axis represents impedance (Ω) and thehorizontal axis represents frequency (Hz).

As illustrated in FIG. 2A, the termination circuit 170 is constitutedby, for example, an LC series resonant circuit including an inductor 200and a capacitor 210, which are connected in series. The LC seriesresonant circuit has a characteristic in which impedance is locally lowat a resonant frequency f₀=1/(2π√LC) (Hz), where L denotes theinductance value of the inductor and C denotes the capacitance value ofthe capacitor. Accordingly, if the transmit frequency band ranges fromfmin to fmax (Hz), as illustrated in FIG. 3A, the constants of theinductor 200 and the capacitor 210 are set so that the resonantfrequency f_(T1) of the termination circuit 170 is included in thesecond-order harmonic band of 2fmin to 2fmax (Hz) of a transmit signal.Thus, the second-order harmonic can be selectively short-circuited toground potential. Furthermore, the Q value of the termination circuit170 is preferably set so that the impedance is sufficiently high and thesignal loss can be reduced within the transmit frequency band. Theresonant frequency f_(T1) may be set to a frequency that is twice ashigh as the center frequency of the transmit frequency band, forexample, or may be shifted to a higher or lower frequency than thefrequency that is twice as high as the center frequency, taking intoaccount impedance variations or signal loss within the transmitfrequency band.

The filter circuit 180 is connected in series with the transmission pathL between the collector of the upper transistor 111 and the matchingnetwork 161 along the transmission path L. In this embodiment, thefilter circuit 180 is constituted by, for example, a tank circuit (LCparallel resonant circuit) that makes the third-order harmonic of theamplified signal open-circuited.

FIG. 2B illustrates a specific example of the filter circuit 180, andFIG. 3B is a graph illustrating the frequency characteristic of theimpedance of the filter circuit 180. In the graph illustrated in FIG.3B, the vertical axis represents impedance (Ω) and the horizontal axisrepresents frequency (Hz).

As illustrated in FIG. 2B, the filter circuit 180 is constituted by, forexample, an LC parallel resonant circuit including an inductor 201 and acapacitor 211, which are connected in parallel. The LC parallel resonantcircuit has a characteristic in which impedance is locally high at aresonant frequency f₀=1/(2π√LC) (Hz), where L denotes the inductancevalue of the inductor and C denotes the capacitance value of thecapacitor. Accordingly, as illustrated in FIG. 3B, the constants of theinductor 201 and the capacitor 211 are set so that the resonantfrequency f_(F1) of the filter circuit 180 is included in thethird-order harmonic band of 3fmin to 3fmax (Hz) of a transmit signal.Thus, the third-order harmonic can be selectively made open-circuited.Furthermore, the Q value of the filter circuit 180 is preferably set sothat the impedance is sufficiently low and the signal loss can bereduced within the transmit frequency band. The resonant frequencyf_(F1) may be set to a frequency that is three times as high as thecenter frequency of the transmit frequency band, for example, or may beshifted to a higher or lower frequency than the frequency that is threetimes as high as the center frequency, taking into account impedancevariations or signal loss within the transmit frequency band.

The elements included in the termination circuit 170 and the filtercircuit 180 may be disposed on a semiconductor substrate having thetransistors 110 and 111 and so on. Alternatively, for example, thecapacitors 210 and 211 may be disposed on the semiconductor substrate,and the inductors 200 and 201 may be disposed on a module substrate onwhich the semiconductor substrate is mounted. In FIG. 1, in terms of thefunctional configuration, the filter circuit 180 and the matchingnetwork 161 are separately illustrated. However, the filter circuit 180and the matching network 161 may not necessarily be separately formed,and, for example, the matching network 161 may have the function of thefilter circuit 180.

As described above, among harmonics outputted from the amplifier, thesecond-order harmonic, which is part of the even-order harmonics, isshort-circuited and the third-order harmonic, which is part of theodd-order harmonics, is made open-circuited, thereby making the waveformof the collector current of the transistors 110 and 111 close to ahalf-wave rectified waveform and making the waveform of the collectorvoltage of the transistors 110 and 111 close to a rectangular waveform.Thus, the amplifier operates in a so-called class-F mode.

FIG. 4 illustrates the waveforms of a collector voltage Vc (solid line)and a collector current Ic (dotted line) of the amplifier when operatingin a class-F mode. As illustrated in FIG. 4, in the class-F operation,phase adjustment is performed so that the peaks of the voltage waveformdo not overlap the peaks of the current waveform. This adjustmentreduces the time period in which the waveform of the collector currentIc and the waveform of the collector voltage Vc overlap. As a result,the power consumption (=collector current Ic×collector voltage Vc) ofthe amplifier ideally becomes 0 W. In the class-F operation, therefore,the power-added efficiency of the power amplifier circuit 100A isimproved.

The harmonics to be controlled to be short-circuited or madeopen-circuited are not limited to the second-order harmonic and thethird-order harmonic. Any of the second and higher even-order harmonicsmay be short-circuited, and any of the third and higher odd-orderharmonics may be made open-circuited.

In this embodiment, a common current flows through the lower transistor110 and the upper transistor 111. That is, the capacitance value of thecapacitor 141 and the inductance values of the inductors 150 and 152 aresufficiently large, and their impedances are assumed to be negligible.In this case, the collector current flowing through the lower transistor110 is equal to the collector current flowing through the uppertransistor 111. Further, the collector voltage waveform of the lowertransistor 110 has an amplitude that is about half the collector voltagewaveform of the upper transistor 111, and the emitter voltage waveformof the upper transistor 111 is equal to the collector voltage waveformof the lower transistor 110. Accordingly, the collector-emitter voltagewaveform of the upper transistor 111 is equal to the collector-emittervoltage waveform of the lower transistor 110. In this embodiment,therefore, the harmonics of the output of the upper transistor 111 arecontrolled, thereby allowing harmonics caused by the lower transistor110 to be also controlled at the same time.

As described above, the power amplifier circuit 100A can output theamplified signal RFout having a voltage amplitude that is about twice ashigh as that in a configuration in which transistors are not verticallyconnected to each other, and thus the maximum output power can beincreased. In addition, since the power amplifier circuit 100A includesthe termination circuit 170 that short-circuits the second-orderharmonic to ground potential, and the filter circuit 180 that makes thethird-order harmonic open-circuited, the amplifier can operate in aclass-F mode. Thus, the power-added efficiency of the power amplifiercircuit 100A can be improved and the direct current power consumptioncan be reduced without controlling the harmonics of the output of thelower transistor 110.

Furthermore, in the power amplifier circuit 100A including both thetermination circuit 170 and the filter circuit 180, the voltage andcurrent waveforms of the amplifier are shaped, compared to aconfiguration including one of the termination circuit 170 and thefilter circuit 180. Thus, the power-added efficiency is furtherimproved. The power amplifier circuit 100A may not necessarily includeone of the termination circuit 170 and the filter circuit 180.

In the power amplifier circuit 100A described above, the terminationcircuit 170 is connected to the collector of the upper transistor 111.However, a termination circuit may be connected to the collector of thelower transistor 110 instead of the upper transistor 111.

In FIG. 1, furthermore, the power amplifier circuit 100A includes onestage of amplifier. However, the power amplifier circuit 100A mayinclude two or more stages of amplifiers including, for example, aninitial stage (drive stage) and a subsequent stage (power stage). In apower amplifier circuit including two or more stages of amplifiers,preferably, the configuration illustrated in FIG. 1 is applied to, forexample, the amplifier in the final stage, where the output power of asignal is the highest, and the other amplifier or amplifiers have aconfiguration in which transistors are not vertically connected to eachother. This configuration suppresses an increase in circuit size,compared to the case where the configuration illustrated in FIG. 1 isapplied to all amplifiers. It should be noted that the configurationillustrated in FIG. 1 may be applied to an amplifier other than theamplifier in the final stage, such as an amplifier for which high gainis required.

The number of transistors vertically connected to each other is notlimited to two and may be three or more. For example, when N transistors(N is an integer of 2 or more) are vertically connected to each other,the signal amplitude at the collector of the uppermost transistor isabout N times as high as the signal amplitude at the collector of onetransistor.

FIG. 5 illustrates an example configuration of a power amplifier circuit100B according to a second embodiment of the present disclosure. In thefollowing embodiments, the same or substantially the same elements asthose of the power amplifier circuit 100A are denoted by the samenumerals, and will not be repeatedly described. Further, features commonto the first embodiment will not be described, and only the differenceswill be described. In particular, similar operational effects achievedwith similar configurations will not be described again in theindividual embodiments.

In the power amplifier circuit 100B, as illustrated in FIG. 5, atermination circuit 171 is connected also to the output of the lowertransistor 110, in addition to the upper transistor 111. The terminationcircuit 171 (first termination circuit) is disposed so as to branch offfrom a node between the collector of the lower transistor 110 and theemitter of the upper transistor 111 along the transmission path L. Inthis embodiment, the termination circuit 171 has the same resonantfrequency as the termination circuit 170 (second termination circuit)and is configured to short-circuit the second-order harmonic of theamplified signal RFout to ground potential. The specific configurationof the termination circuit 171 can be similar to that of the terminationcircuit 170 illustrated in, for example, FIG. 2A, and will not bedescribed in detail.

The lower and upper transistors 110 and 111 perform basically the sameoperation. The symmetry of the lower and upper transistors 110 and 111may fail depending on the settings of the voltage regulator circuit 130or when the impedance of the inductor 150 or 152 or the capacitor 141 isnot sufficiently high. Even in this case, in the power amplifier circuit100B, each of the lower and upper transistors 110 and 111 is connectedto a termination circuit, and, thus, the voltage and current waveformsof the collectors of the transistors 110 and 111 can be appropriatelyshaped. In addition, the termination circuit 171 also short-circuits thesecond-order harmonic that appears at the emitter of the uppertransistor 111 to ground potential. Accordingly, the shaping of thevoltage and current waveforms of the transistor 111 is supported.

In FIG. 5, an end of the termination circuit 171 is connected betweenthe collector of the transistor 110 and the capacitor 141. However, theconnection position of the end of the termination circuit 171 is notlimited to this, and the end of the termination circuit 171 may beconnected to any node between the collector of the transistor 110 andthe emitter of the transistor 111.

FIG. 6 illustrates an example configuration of a power amplifier circuit100C according to a third embodiment of the present disclosure. Asillustrated in FIG. 6, unlike the power amplifier circuit 100B, thepower amplifier circuit 100C includes a termination circuit 172 insteadof the termination circuit 171.

The termination circuit 172 includes part of the inductor 152, whichconnects the emitter of the upper transistor 111 to ground, as aninductor included in an LC series resonant circuit. Specifically, thetermination circuit 172 includes part of the inductor 152, and acapacitor 212 (second capacitor) that branches off from a point on acoil conductor included in the inductor 152 and that is connected toground. If the inductance value of one of the two divided portions ofthe inductor 152 connected to ground has sufficiently high impedance forthe fundamental, the impedance appears to be an open circuit for thefundamental. In the termination circuit 172, thus, part of the inductor152 and the capacitor 212 function as an LC series resonant circuit. Theinductance value used to determine the resonant frequency of the LCseries resonant circuit corresponds to the inductance value determinedwhen the two divided portions of the inductor 152 are connected inparallel. The function of the termination circuit 172 is similar to thatof the termination circuit 171, and will not be described in detail.

With the configuration described above, in the power amplifier circuit100C, the termination circuit 172 is constituted by fewer elements thanin the power amplifier circuit 100B and can achieve advantages similarto those of the power amplifier circuit 100B.

In FIG. 6, part of the inductor 152 functions as an inductance componentof the termination circuit 172, by way of example. Alternatively, forexample, part of the inductor 150 may function as an inductancecomponent of a termination circuit. In this case, a capacitorcorresponding to the capacitor 212 may branch off from a point on a coilconductor included in the inductor 150 and may be connected to ground.

In the power amplifier circuits 100B and 100C described above, twotermination circuits have an equal resonant frequency. However, thesetermination circuits may have different resonant frequencies. A fourthembodiment (a power amplifier circuit 100D) provides, for example, aconfiguration similar to that of the power amplifier circuit 100Billustrated in FIG. 5, in which the two termination circuits 170 and 171respectively have resonant frequencies f_(T1) and f_(T2) that aredifferent.

FIG. 7 is a graph illustrating the frequency characteristic of theattenuation of an output signal in the power amplifier circuit 100D. Inthis embodiment, the resonant frequencies f_(T1) and f_(T2) of thetermination circuits 170 and 171 are different. Thus, in FIG. 7, thevertical axis represents attenuation (dB) instead of impedance.

As illustrated in FIG. 7, in this embodiment, the resonant frequencyf_(T1) of the termination circuit 170 is set to a frequency that isabout twice as high as the center frequency of the transmit frequencyband, and the resonant frequency f_(T2) of the termination circuit 171is set to a frequency higher than the upper limit 2fmax (Hz) of thesecond-order harmonic band. This setting allows the second-orderharmonic to be attenuated over a wider range than that for aconfiguration including a single termination circuit (see the brokenline). Accordingly, the second-order harmonic is sufficientlyshort-circuited to ground potential over a wider frequency range thanthat in a configuration including a single termination circuit. Thus,the power-added efficiency is expected to be further improved. Thisembodiment is suitable for, for example, a comparatively wide transmitfrequency band.

The method for shifting the resonant frequencies of the two terminationcircuits is not limited to that described above. As described above, oneof the resonant frequencies may be shifted to a higher frequency thanthe center frequency of the second-order harmonic, thereby suppressingthe attenuation of the fundamental frequency component to betransmitted, compared to the case where the one of the resonantfrequencies may be shifted to a lower frequency.

FIG. 8 illustrates an example configuration of a power amplifier circuit100E according to a fifth embodiment of the present disclosure. Asillustrated in FIG. 8, unlike the power amplifier circuit 100B, thepower amplifier circuit further includes termination circuits 173 and174.

The termination circuit 173 is connected in parallel with thetermination circuit 170. The termination circuit 174 is connected inparallel with the termination circuit 171. In this embodiment, the fourtermination circuits 170, 171, 173, and 174 have resonant frequenciesset to around the second-order harmonic band and shifted from eachother.

FIG. 9 is a graph illustrating the frequency characteristic of theattenuation of an output signal in the power amplifier circuit 100E.

As illustrated in FIG. 9, in this embodiment, the termination circuits170, 171, 173, and 174 respectively have resonant frequencies f_(T1),f_(T2), f_(T3), and f_(T4) set to around the second-order harmonic bandsuch that the resonant frequency f_(T2) is higher than the resonantfrequency f_(T1), the resonant frequency f_(T3) is higher than theresonant frequency f_(T2), and the resonant frequency f_(T4) is higherthan the resonant frequency f_(T3). This setting allows the second-orderharmonic to be attenuated over a wider range than that for the poweramplifier circuit 100D including the two termination circuits 170 and171. Thus, the power-added efficiency of the power amplifier circuit100E can be improved over a wider range than that for the poweramplifier circuit 100D.

FIG. 10 illustrates an example configuration of a power amplifiercircuit 100F according to a sixth embodiment of the present disclosure.As illustrated in FIG. 10, unlike the power amplifier circuit 100E, thepower amplifier circuit 100F includes termination circuits 175 and 176that short-circuit the fourth-order harmonic, instead of the terminationcircuits 173 and 174 that short-circuit the second-order harmonic.

The termination circuit 175 (fourth termination circuit) is connected inparallel with the termination circuit 170. The termination circuit 176(third termination circuit) is connected in parallel with thetermination circuit 171. The termination circuits 175 and 176 haveresonant frequencies set to around the fourth-order harmonic band. Thissetting can make the harmonic band to be attenuated wider than that forthe power amplifier circuit 100B including two termination circuits. Inaddition, unlike the power amplifier circuit 100E in which the fourtermination circuits 170, 171, 173, and 174 short-circuit thesecond-order harmonic, in the power amplifier circuit 100F, both thesecond-order harmonic and the fourth-order harmonic are short-circuited,and thus, the voltage and current waveforms of the amplifier may becomemore ideal. Accordingly, the power-added efficiency is expected to befurther improved.

As described above, the harmonics to be short-circuited by a pluralityof termination circuits are not limited to the second-order harmonic,and may include any other even-order harmonic. The termination circuit170 and the termination circuit 171 may have an equal resonant frequencyor different resonant frequencies, and the termination circuit 175 andthe termination circuit 176 may have an equal resonant frequency ordifferent resonant frequencies.

FIG. 11 illustrates an example configuration of a power amplifiercircuit 100G according to a seventh embodiment of the presentdisclosure. As illustrated in FIG. 11, unlike the power amplifiercircuit 100A, the power amplifier circuit 100G includes a filter circuit181 instead of the filter circuit 180, and a capacitor 143 instead ofthe capacitor 141.

The filter circuit 181 is disposed along the transmission path L betweenthe collector of the lower transistor 110 and the emitter of the uppertransistor 111. Specifically, the filter circuit 181 is constituted byan LC parallel resonant circuit including an inductor 202 (secondinductor) and a capacitor 212, which are connected in parallel. Thefilter circuit 181 has a resonant frequency set so as to be included inthe third-order harmonic band, for example. Specifically, the resonantfrequency is determined by the inductance value of the inductor 202 andthe capacitance value determined when the capacitor 212 and thecapacitor 143 are connected in series.

The capacitor 143 is disposed between the inductor 202 and the collectorof the lower transistor 110. Like the capacitor 141 according to theembodiments described above, the capacitor 143 (third capacitor) has afunction of cutting off the upper transistor 111 and the lowertransistor 110 for direct current. The capacitor 143 has a capacitancevalue set to be sufficiently larger than the capacitance value of thecapacitor 212. Accordingly, the resonant frequency of the filter circuit181 is determined by the capacitance value of the capacitor 212. Thatis, the effect of the capacitance value of the capacitor 143 on theresonant frequency of the filter circuit 181 can be reduced.

In this manner, a filter circuit that makes the third-order harmonicopen-circuited is not necessarily positioned between the uppertransistor 111 and the output terminal T, and may be positioned betweenthe lower transistor 110 and the upper transistor 111. With thisconfiguration, the power amplifier circuit 100G can achieve advantagessimilar to those of the power amplifier circuit 100A.

FIG. 12 illustrates an example configuration of a power amplifiercircuit 100H according to an eighth embodiment of the presentdisclosure. As illustrated in FIG. 12, the power amplifier circuit 100Hincludes both the filter circuit 180 illustrated in FIG. 1 and thefilter circuit 181 illustrated in FIG. 11.

The power amplifier circuit 100H including the two filter circuits 180(second filter circuit) and 181 (first filter circuit) can separatelycontrol the voltage and current waveforms of the collector of the uppertransistor 111 and the voltage and current waveforms of the collector ofthe lower transistor 110. The resonant frequency of the filter circuit180 and the resonant frequency of the filter circuit 181 may be equal ordifferent.

FIG. 13 is a graph illustrating the frequency characteristic of thetransmission attenuation of an output signal in the power amplifiercircuit 100H. In the graph illustrated in FIG. 13, the vertical axisrepresents the transmission attenuation (dB) of the filter circuits 180and 181. The illustrated graph is obtained when the resonant frequencyof the filter circuit 180 and the resonant frequency of the filtercircuit 181 are set to be different.

As illustrated in FIG. 13, the filter circuits 180 and 181 respectivelyhave resonant frequencies f_(F1) and f_(F2) set so as to be included inthe third-order harmonic band. In this embodiment, this setting allowsthe transmission of the third-order harmonic to be suppressed over awider range than that for a configuration including a single filtercircuit.

The power amplifier circuits 100A to 100H with improved power-addedefficiency that can increase the maximum output power have beendescribed. The embodiments described above provide a configuration inwhich an even-order harmonic is short-circuited to ground potential andan odd-order harmonic is made open-circuited, thereby allowing theamplifier to operate in a class-F mode. Alternatively, a power amplifiercircuit may be configured such that an odd-order harmonic isshort-circuited to ground potential and an even-order harmonic is madeopen-circuited. For example, the power amplifier circuit 100A is takenas an example. The termination circuit 170 may short-circuit thethird-order harmonic to ground potential, and the filter circuit 180 maymake the second-order harmonic open-circuited. In this case, the currentwaveform of the amplifier is close to a rectangular waveform, and thevoltage waveform of the amplifier is close to a half-wave rectifiedwaveform. Thus, the amplifier operates in an inverse class-F mode. Alsoin the inverse class-F operation, power consumption can be reduced, andpower-added efficiency can be improved.

In the class-F operation, the current waveform is a half-wave rectifiedwaveform, which may cause the parasitic resistance component of atransistor to affect power amplification characteristics. However, thevoltage waveform is a rectangular waveform, which can reduce the risk ofexceeding a withstand voltage of a transistor. In the inverse class-Foperation, in contrast, the voltage waveform is a half-wave rectifiedwaveform, which may cause a risk of exceeding a withstand voltage of atransistor. However, the current waveform is a rectangular waveform,resulting in reduced effect on the power amplification characteristicscaused by the parasitic resistance component.

Exemplary embodiments of the present disclosure have been described. Thepower amplifier circuits 100A to 100H include the transistor 110 havinga first terminal, a second terminal, and a third terminal, wherein thepower supply voltage Vcc1 is supplied to the first terminal, the secondterminal is connected to ground, and an input signal is supplied to thethird terminal; the capacitor 141; the transistor 111 having a firstterminal, a second terminal, and a third terminal, wherein the powersupply voltage Vcc2 is supplied to the first terminal, an amplifiedsignal obtained by amplifying the input signal is outputted to theoutput terminal T from the first terminal, the second terminal isconnected to the first terminal of the transistor 110 via the capacitor141, and a driving voltage is supplied to the third terminal; theinductor 152 that connects the second terminal of the transistor 111 toground; the voltage regulator circuit 130 that adjusts the drivingvoltage; and at least one termination circuit 170 that short-circuitsone of an even-order harmonic or odd-order harmonic of the amplifiedsignal to ground potential. The at least one termination circuit 170 isdisposed so as to branch off from a node along the transmission path Lextending from the first terminal of the transistor 110 to the outputterminal T through the capacitor 141 and the transistor 111. With thisconfiguration, the power amplifier circuits 100A to 100H can output anamplified signal having a voltage amplitude that is about twice as highas that in a configuration in which transistors are not verticallyconnected to each other, and can allow the amplifier to operate in aclass-F mode. Accordingly, the power amplifier circuits 100A to 100H canbe provided with improved power-added efficiency while increasing themaximum output power.

In the power amplifier circuit 100C, furthermore, the terminationcircuit 172 includes the capacitor 212 that branches off from a point ona coil conductor included in the inductor 152 and that is connected toground. With this configuration, in the power amplifier circuit 100C,the termination circuit 172 can be constituted by fewer elements than inthe power amplifier circuit 100B.

The power amplifier circuits 100A to 100H further includes at least onefilter circuit 180 (181) that makes the other of the even-order harmonicor odd-order harmonic of the amplified signal open-circuited. The atleast one filter circuit 180 (181) is connected in series along thetransmission path L between the first terminal of the transistor 110 andthe output terminal T. With this configuration, in the power amplifiercircuits 100A to 100H, the waveforms of the collector voltage andcollector current of the transistors 110 and 111 can be shaped, comparedto a configuration not including the filter circuit 180 (181). Thus, thepower-added efficiency is further improved.

Although the position of the filter circuit 181 is not limited, as inthe power amplifier circuits 100G and 100H, for example, the filtercircuit 181 may be positioned between the transistor 110 and thetransistor 111 and may include the capacitor 212 and the inductor 202,which are connected in parallel.

Further, the power amplifier circuits 100B to 100F includes thetermination circuit 171 (172) branching off from a node between thefirst terminal of the transistor 110 and the second terminal of thetransistor 111 along the transmission path L, and the terminationcircuit 170 branching off from a node between the first terminal of thetransistor 111 and the output terminal T along the transmission path L.Each of the termination circuit 171 (172) and the termination circuit170 short-circuits the second-order harmonic to ground potential. Withthis configuration, even if the symmetry of the lower and uppertransistors 110 and 111 fails, the voltage and current waveforms can beappropriately shaped.

The power amplifier circuit 100F further includes the terminationcircuit 176 connected in parallel with the termination circuit 171, andthe termination circuit 175 connected in parallel with the terminationcircuit 170. Each of the termination circuit 176 and the terminationcircuit 175 short-circuits the fourth-order harmonic to groundpotential. With this configuration, both the second-order harmonic andthe fourth-order harmonic are short-circuited, and the voltage andcurrent waveforms of the amplifier may become more ideal. Thepower-added efficiency is expected to be further improved.

Further, the power amplifier circuit 100H includes the filter circuit181 connected in series along the transmission path L between the firstterminal of the transistor 110 and the second terminal of the transistor111, and the filter circuit 180 connected in series along thetransmission path L between the first terminal of the transistor 111 andthe output terminal T. Each of the filter circuit 181 and the filtercircuit 180 makes the third-order harmonic open-circuited. Thisconfiguration allows the transmission of the third-order harmonic to besuppressed over a wider range than that for a configuration including asingle filter circuit.

Furthermore, each of the termination circuits described above mayshort-circuit an odd-order harmonic to ground potential, instead of aneven-order harmonic. Likewise, each of the filter circuits describedabove may make an even-order harmonic open-circuited, instead of anodd-order harmonic. With this configuration, the current waveform of theamplifier is close to a rectangular waveform, and the voltage waveformof the amplifier is close to a half-wave rectified waveform. Thus, theamplifier operates in an inverse class-F mode. Accordingly, even theconfiguration described above can improve the power-added efficiency ofthe power amplifier circuit.

The embodiments described above are intended to help easily understandthe present disclosure, and are not to be used to construe the presentdisclosure in a limiting fashion. Various modifications or improvementscan be made to the present disclosure without departing from the gist ofthe present disclosure, and equivalents thereof are also included in thepresent disclosure. That is, the embodiments may be appropriatelymodified in design by those skilled in the art, and such modificationsalso fall within the scope of the present disclosure so long as themodifications include the features of the present disclosure. Forexample, the elements included in the embodiments and the arrangement,materials, conditions, shapes, sizes, and the like thereof are notlimited to those described in the illustrated examples, but can bemodified as appropriate. Furthermore, the elements included in theembodiments can be combined to the extent that it is technicallypossible to do so, and such combinations of elements also fall withinthe scope of the present disclosure so long as the combinations ofelements include the features of the present disclosure.

While preferred embodiments of the disclosure have been described above,it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the disclosure. The scope of the disclosure, therefore, isto be determined solely by the following claims.

What is claimed is:
 1. A power amplifier circuit comprising: a lowertransistor having a first terminal, a second terminal, and a thirdterminal, wherein a first power supply voltage is supplied to the firstterminal, the second terminal is connected to ground, and an inputsignal is supplied to the third terminal; a first capacitor; an uppertransistor having a first terminal, a second terminal, and a thirdterminal, wherein a second power supply voltage is supplied to the firstterminal of the upper transistor, an amplified signal obtained byamplifying the input signal is output to an output terminal from thefirst terminal of the upper transistor, the second terminal of the uppertransistor is connected to the first terminal of the lower transistorvia the first capacitor, and a driving voltage is supplied to the thirdterminal of the upper transistor; a first inductor that connects thesecond terminal of the upper transistor to ground; a voltage regulatorcircuit; and at least one termination circuit that short-circuits one ofan even-order harmonic or an odd-order harmonic of the amplified signalto ground potential, the at least one termination circuit being disposedso as to branch off from a node along a transmission path extending fromthe first terminal of the lower transistor to the output terminalthrough the first capacitor and the upper transistor.
 2. The poweramplifier circuit according to claim 1, wherein the at least onetermination circuit includes a second capacitor that branches off from anode on a coil conductor included in the first inductor, the secondcapacitor being connected to ground.
 3. The power amplifier circuitaccording to claim 1, further comprising at least one filter circuitthat makes the other of the even-order harmonic or odd-order harmonic ofthe amplified signal open-circuited, the at least one filter circuitbeing connected in series along the transmission path between the firstterminal of the lower transistor and the output terminal.
 4. The poweramplifier circuit according to claim 2, further comprising at least onefilter circuit that makes the other of the even-order harmonic orodd-order harmonic of the amplified signal open-circuited, the at leastone filter circuit being connected in series along the transmission pathbetween the first terminal of the lower transistor and the outputterminal.
 5. The power amplifier circuit according to claim 3, furthercomprising a second inductor and a third capacitor, the second inductorand the third capacitor being connected in series with each other andbeing connected in parallel with the first capacitor.
 6. The poweramplifier circuit according to claim 4, further comprising a secondinductor and a third capacitor, the second inductor and the thirdcapacitor being connected in series with each other and being connectedin parallel with the first capacitor.
 7. The power amplifier circuitaccording to claim 1, wherein the at least one termination circuitincludes a first termination circuit branching off from a node betweenthe first terminal of the lower transistor and the second terminal ofthe upper transistor along the transmission path, and a secondtermination circuit branching off from a node between the first terminalof the upper transistor and the output terminal along the transmissionpath, and wherein each of the first termination circuit and the secondtermination circuit short-circuits a second-order harmonic to groundpotential.
 8. The power amplifier circuit according to claim 7, whereinthe at least one termination circuit further includes a thirdtermination circuit connected in parallel with the first terminationcircuit, and a fourth termination circuit connected in parallel with thesecond termination circuit, and wherein each of the third terminationcircuit and the fourth termination circuit short-circuits a fourth-orderharmonic to ground potential.
 9. The power amplifier circuit accordingto claim 2, wherein the at least one termination circuit includes afirst termination circuit branching off from a node between the firstterminal of the lower transistor and the second terminal of the uppertransistor along the transmission path, and a second termination circuitbranching off from a node between the first terminal of the uppertransistor and the output terminal along the transmission path, andwherein each of the first termination circuit and the second terminationcircuit short-circuits a second-order harmonic to ground potential. 10.The power amplifier circuit according to claim 9, wherein the at leastone termination circuit further includes a third termination circuitconnected in parallel with the first termination circuit, and a fourthtermination circuit connected in parallel with the second terminationcircuit, and wherein each of the third termination circuit and thefourth termination circuit short-circuits a fourth-order harmonic toground potential.
 11. The power amplifier circuit according to claim 3,wherein the at least one termination circuit includes a firsttermination circuit branching off from a node between the first terminalof the lower transistor and the second terminal of the upper transistoralong the transmission path, and a second termination circuit branchingoff from a node between the first terminal of the upper transistor andthe output terminal along the transmission path, and wherein each of thefirst termination circuit and the second termination circuitshort-circuits a second-order harmonic to ground potential.
 12. Thepower amplifier circuit according to claim 9, wherein the at least onetermination circuit further includes a third termination circuitconnected in parallel with the first termination circuit, and a fourthtermination circuit connected in parallel with the second terminationcircuit, and wherein each of the third termination circuit and thefourth termination circuit short-circuits a fourth-order harmonic toground potential.
 13. The power amplifier circuit according to claim 3,wherein the at least one filter circuit includes a first filter circuitconnected in series along the transmission path between the firstterminal of the lower transistor and the second terminal of the uppertransistor, and a second filter circuit connected in series along thetransmission path between the first terminal of the upper transistor andthe output terminal, and wherein each of the first filter circuit andthe second filter circuit makes a third-order harmonic open-circuited.14. The power amplifier circuit according to claim 1, wherein the atleast one termination circuit includes a first termination circuitbranching off from a node between the first terminal of the lowertransistor and the second terminal of the upper transistor along thetransmission path, and a second termination circuit branching off from anode between the first terminal of the upper transistor and the outputterminal along the transmission path, and wherein each of the firsttermination circuit and the second termination circuit short-circuits athird-order harmonic to ground potential.
 15. The power amplifiercircuit according to claim 2, wherein the at least one terminationcircuit includes a first termination circuit branching off from a nodebetween the first terminal of the lower transistor and the secondterminal of the upper transistor along the transmission path, and asecond termination circuit branching off from a node between the firstterminal of the upper transistor and the output terminal along thetransmission path, and wherein each of the first termination circuit andthe second termination circuit short-circuits a third-order harmonic toground potential.
 16. The power amplifier circuit according to claim 3,wherein the at least one termination circuit includes a firsttermination circuit branching off from a node between the first terminalof the lower transistor and the second terminal of the upper transistoralong the transmission path, and a second termination circuit branchingoff from a node between the first terminal of the upper transistor andthe output terminal along the transmission path, and wherein each of thefirst termination circuit and the second termination circuitshort-circuits a third-order harmonic to ground potential.
 17. The poweramplifier circuit according to claim 3, wherein the at least one filtercircuit includes a first filter circuit connected in series along thetransmission path between the first terminal of the lower transistor andthe second terminal of the upper transistor, and a second filter circuitconnected in series along the transmission path between the firstterminal of the upper transistor and the output terminal, and whereineach of the first filter circuit and the second filter circuit makes asecond-order harmonic open-circuited.
 18. The power amplifier circuitaccording to claim 1, wherein: the first terminal of the lowertransistor is a collector or a drain, the second terminal of the lowertransistor is an emitter or a source, and the third terminal of thelower transistor is a base or a gate.
 19. The power amplifier circuitaccording to claim 1, wherein: the first terminal of the uppertransistor is a collector or a drain, the second terminal of the uppertransistor is an emitter or a source, and the third terminal of theupper transistor is a base or a gate.